How to determine the AC withstand voltage test voltage?

The hipot test can effectively test whether the overvoltage that the tested product can withstand is within the specified value, so as to avoid some safety conditions in the working process of the instrument in the future. Founded in 1993, Aino Instrument is mainly engaged in the R&D and production of withstand voltage insulation testers, electrical safety performance testing instruments, AC and DC power supplies, power supply equipment, precision measuring instruments and automatic measurement and control systems. Aino Instruments has established two business divisions in Qingdao and Jinan, China.

Aino Instrument Co., Ltd. has always sincerely served the production lines and laboratories of household appliances, motors, information equipment, switching power supplies, power electronics, medical equipment, lamps and lighting, emerging energy, automobiles and high-speed railways and other industrial enterprises, and has won the long-term trust of customers such as national, provincial and municipal quality inspection institutions and professional certification enterprises.

In the AC withstand voltage test, the key issue is to correctly select the value of the test voltage, on the one hand, it is required to ensure the insulation level, and on the other hand, it is necessary to consider the insulation deterioration caused by the test voltage is too high. In general, the following factors should be considered.

1. The value, duration and number of overvoltages that may be generated on the tested product. If the possibility of the test product being subjected to a high overvoltage is very small, it is not necessary to use an excessively high test voltage; If the test product (such as a generator directly connected to an overhead line) may be subjected to a high overvoltage, the value of the test voltage should be increased appropriately.

2. The level of insulation used in the design of electrical equipment.

3. The condition of equipment insulation. Due to the influence of various conditions in the operation of the equipment, the insulation gradually deteriorates and the insulation performance decreases, so the degree of insulation damage and the operating life should be taken into account when determining the test voltage. For example, the test voltage of the equipment in operation should be 75 90 at the factory.

How the AC test voltage is generated.

The power frequency high voltage is usually generated by a high-voltage test transformer; For the test product with large capacitance, a series resonant loop can be used to generate high voltage; For power transformers, voltage transformers and other tested products with windings, 100Hz and 300Hz intermediate frequency power supply can be used to excite the windings on the low-voltage side to generate high voltage in the high-voltage windings.

According to the standard, the voltage standard of the AC withstand bridge Zheng test of the motor should be as follows:

1. For motors with rated voltage not exceeding 1000V, the withstand voltage test voltage should be 1 minute.

2. For motors with rated voltage greater than 1000V, the withstand voltage test voltage should be 3kV and the duration should be 1 minute.

3. For motors with higher voltage levels, the withstand voltage test should be carried out according to the rated voltage level of the motor.

Uses of AC withstand voltage test:

AC withstand voltage test is the most effective and direct method to identify the degree of insulation and strong backup signal cover of power equipment, and is an important part of preventive test. In addition, because the AC withstand voltage test voltage is generally higher than the operating voltage, so after passing the test, the equipment has a large safety margin, so the AC withstand voltage test is an important means to ensure the safe operation of power equipment.

Hipot test is a non-destructive test that is used to check whether the insulation ability of a product is acceptable under the transient high voltage that often occurs. It applies high voltage to the equipment under test for a certain period of time to ensure that the insulation performance of the equipment is strong enough.

Test voltageMost safety standards allow the use of AC or straight dissipative current voltages in hipot testing. If an AC test voltage is used, the insulating bureau to be tested is subjected to maximum pressure when the voltage peak is reached, regardless of whether it is a positive or negative polarity peak. <>

In order to ensure the safe and smooth progress of the test work, some key points in the test operation need to be paid attention to

Before the test, the test voltage of the tested cable should be understood, and other test items of the tested cable and the previous test results should be understood. If it is found that the tested cable is defective or abnormal, the AC withstand voltage test should be carried out after elimination. According to the capacitance of the cable.

and test voltage to estimate the size of the test current, judge whether the capacity of the test transformer is sufficient, and consider the setting value of overcurrent protection (generally should be set to the capacitance current of the tested cable.

times). The test site should be fenced or fenced, hung up signs, and sent a special person to supervise it. The test product should be disconnected from other equipment, and keep a sufficient safety distance, and when the distance is insufficient, an insulating baffle or other protective measures should be considered.

Before the test, the surface of the tested cable should be wiped clean.

After the test wiring is connected, it should be checked by an experienced person and confirmed that it is correct before it can be prepared for boosting.

Adjust the variable frequency series resonant withstand voltage test device to protect the ball gap so that the discharge voltage is 110% 120% of the test, and there should be no obvious difference in the continuous test for three times, and check the reliability of the overcurrent protection action.

Before pressurizing, first check whether the regulator is in the zero position. The voltage regulator can only be boosted at the zero position, and each other should be reminded to pay attention to safety when boosting.

The variable frequency series resonant withstand voltage test device should not only monitor the voltmeter during the step-up process.

The ammeter should also be monitored.

and the current of the test piece. When boosting, it should be boosted at a constant speed, not too fast. When the specified test voltage is raised, the time is calculated, and when the time is up, the voltage is slowly and evenly lowered.

It is not allowed to jump the power switch first without stepping down. Because the power switch jumps without stepping down is equivalent to doing an operation wave test for the tested product, it is very likely to damage the equipment insulation.

If it is found that the voltage fluctuates greatly or the tested cable has abnormal sound, smoke, fire, etc., the voltage should be lowered immediately, the power supply should be pulled out, and the grounding wire should be hung on the high-voltage side.

After that, the cause will be identified.

The insulation resistance of the tested cable should be measured before and after the AC withstand voltage test.

When possible, a partial discharge test is also carried out.

The figure shows the schematic diagram of the AC withstand voltage test. The test detects the defects and problems in the insulation performance of the sample under AC high voltage. The state stipulates that if the tested cable can withstand the power frequency test voltage for one minute without breakdown, insulation flashover or other abnormal problems, the cable can be judged to be well insulated.

The function of R1 in the figure is to limit the short-circuit current of the transformer when the tested cable is discharged, so that it is lower than the allowable value, and the voltage gradient of the high-voltage winding needs to be lower than the dangerous value; The function of R2 is to limit the current of the spherical gap discharge; The function of the voltage regulating transformer is to adjust the amplitude of the test voltage and the speed of voltage rise and fall; In terms of the selection of test transformers, single or cascade test transformers can be used, depending on the specific conditions of the test.

Although the AC withstand voltage test has some shortcomings, that is, under the action of higher AC voltage, some weaknesses in the insulation will be more developed (not yet caused by breakdown), and each test will cause new damage accumulation to the insulation (this phenomenon is called the accumulation effect), but this test must also be done. This is because the various non-destructive test methods for electrical equipment insulation, although they can reflect the condition of insulation from different sides and find some defects, the test voltage added by these test methods to the equipment insulation is often lower than the working voltage of the equipment, and the insulation weaknesses cannot be effectively found; DC withstand voltage test, although the test voltage is high, some insulation weaknesses can be found, but because most of the insulation of electrical equipment is a composite insulation structure, under the action of DC test voltage, the voltage is distributed according to resistance, and under the action of AC voltage, it is mainly distributed according to capacitance, so the conditions of DC withstand voltage test are inconsistent with the actual operation of the equipment, and the equivalence is poor.

The AC withstand voltage test is more in line with the actual operation of electrical equipment insulation, so it is often more effective to find insulation weaknesses. For example, it is relatively easy to find the insulation weaknesses of the motor stator winding groove and notch (the DC withstand voltage test is relatively easy to find the insulation defect at the end of the winding), and because of this, the power frequency AC withstand voltage test is a decisive test in the various tests of electrical equipment insulation. It is an appraisal test that finally judges whether the electrical equipment can be put into operation after the previous insulation tests have been carried out and qualified.

The AC withstand voltage test should be selected.

The purpose of the DC withstand voltage test is to test the highest voltage peak that the operation of electrical equipment can withstand;

The purpose of the AC withstand voltage test is to test the dielectric strength of power equipment;

For the cable, it is just a power transmission device, the resistance is extremely low, and it is pointless to test how much voltage it can withstand without heating up; The cable needs to be insulated from the surrounding environment to avoid loss of power resources or danger, so the AC withstand voltage test should be selected.

The new 10kV oil-immersed transformer has a power frequency AC test withstand voltage (AC) of 35kV on the high-voltage side. If the low-voltage side is 400V, the power frequency AC test withstand voltage is 5000V.

The new 10kV dry-type transformer, its power frequency test withstand voltage, there are two kinds:

1. 28kV according to indoor requirements;

2. According to outdoor requirements, it is 35kv. However, more dry transformer manufacturing plants are designed and manufactured according to the 35kV withstand voltage level. The low-voltage 400V side is still 5000V.

Before the test, we should first measure the insulation resistance of the tested electric power cable, and record the data, and then use the AC withstand voltage test equipment ("series resonance") of 20-300Hz to carry out the AC withstand voltage test in accordance with the above requirements, after the test is completed, the cable is fully discharged, and then the insulation resistance value is measured, and the data result should be very similar to the measurement result before the test, and the cable can be considered to be well insulated; Secondly, in the test process, through the fault alarm signal of the series resonance test device, it can also be judged whether the insulation of the cable is good, mainly to observe whether there is a non-human emergency shutdown, flashover fault, etc. in the test process, if it appears, it should be stopped for inspection, check whether the insulation resistance meets the requirements, if it does not meet the requirements, it means that the cable has occurred different degrees of insulation faults, does not meet the requirements of operation, It should be noted that the cable should pay attention to the accumulation effect of the cable when carrying out the AC withstand voltage test. Minimize the damage to the cable caused by the AC withstand voltage.

AC withstand voltage test is a preventive test method for large-capacity and high-voltage operating equipment in the power system, a destructive test for dielectric strength, the method can effectively avoid sudden failure after power operation, causing large-scale power outages, etc., AC withstand voltage test is also called "resonance test", which plays a decisive role in whether the power system can be put into operation.

Withstand voltage test test requirements.

Let's take 10kv cable as an example, combined with the power preventive test specification to talk about the requirements and results of the withstand voltage test, for example: the rated voltage is 18 30kV below the rubber and plastic cable, the test voltage is or 2U0, and the test time is 5-60min.

How to analyze the AC withstand voltage test.

Before the test, we should first measure the insulation resistance of the tested electric power cable, and record the data, and then use the AC withstand voltage test equipment ("series resonance") of 20-300Hz to carry out the AC withstand voltage test in accordance with the above requirements, after the test is completed, the cable is fully discharged, and then the insulation resistance value is measured, and the data result should be very similar to the measurement result before the test, and the cable can be considered to be well insulated; Secondly, in the test process, through the fault alarm signal of the series resonance test device, it can also be judged whether the insulation of the cable is good, mainly to observe whether there is a non-human emergency shutdown, flashover fault, etc. in the test process, if it appears, it should be stopped for inspection, check whether the insulation resistance meets the requirements, if it does not meet the requirements, it means that the cable has occurred different degrees of insulation faults, does not meet the requirements of operation, It should be noted that the cable should pay attention to the accumulation effect of the cable when carrying out the AC withstand voltage test. Minimize the damage to the cable caused by the AC withstand voltage.

Respondent: Huatian Power.

Before the cable AC withstand voltage test, it should be found out whether the other tests are qualified, and the AC withstand voltage test can be done simply after the wearing pants are qualified. The cable to be tested should be disconnected from all the connecting wires of the outside world, and during the test, the high voltage to be measured should be added, and the others should be shorted to the ground.

Before the AC withstand voltage test of the cable, the trace manuscript should be returned to find out whether the other tests are qualified, and the AC withstand voltage test can be done only after it is qualified. The cable to be tested should be disconnected from all the connecting lines of the outside world, and during the test, the high voltage to be measured should be added, and the others should be shorted to the ground.